[DavidNJ]

I actually used kilograms and coverted back...never could keep the English units straight. Matcad does the unit conversions for you though, In this case the constant, g, is the same on both sides so the ratio holds.

However, you are correct, I forgot to convert diameter to radius, so I was off by a factor of 4. This would make the energy equivalent to around 2mph. I knew the number should have been around 4-6 lb*ft²...so I must have been asleep at the wheel here. There is probably another 1-1.5 lb*ft² from the crank, rods, pistons, pins, rings, and bearings.